The invention relates to a sealing arrangement for sealing between two pressure spaces of a turbo-engine or the like, utilizing a brush sealing device non-rotatably anchored at a stator with free bristle ends guided toward a rotor.
From EP-A 0199322, a brush sealing device is known for bridging a gap between two stationary components which are subjected to thermal or other deformations and forces or movements. In this case, the bristles of the brush sealing device are to be freely movably guided at one end with the one component and with the other free end in a joint of the other component. The known case does not concern a brush sealing device which is suitable and constructed for the sealing of a radial gap between a rotor and a stator.
From U.S. RE No. 30,206, a use (FIG. 4) of a brush sealing device as well as a manufacturing process of the sealing device (FIGS. 1 to 3) is known. According to the use, for example, in a turbo-engine, the sealing element, which is constructed as a brush, is to be fixedly anchored on one side at the stator and by means of the other free end is to sit loosely on the rotor. In this manner, differential expansions between the rotor and the stator which particularly are caused thermally from nonsteady operating conditions, are to be sealingly compensated while the seal leakage flow is minimal.
For producing this brush sealing device in this known case, the brush bundle is first folded together and is then inserted on the side of the folding into bores of a first ring and is wired to it. The exterior open ends of the brush bundles, which partially overlap one another in circumferential direction, must then be clamped into a circumferential recess of a second ring which is coaxially assigned to the first ring and are to be welded in there. As a result of the center-coaxial cutting-through of the brush bundle, the remainder of the brush containing the foldings, including the first ring, must then be removed completely so that the remaining brush part which is fixedly bound into the second ring will form the discussed brush sealing device (FIG. 4) having bristle ends which are free toward the outside and sit on the rotor in an unguided manner.
In practice, an important advantage of such a brush sealing device arranged between the rotor and the stator is the fact that, particularly in view of nonsteady operating conditions of a turbo-engine, such as a gas turbine engine, it is capable of compensating thermally caused radial gap changes between the stator and the rotor without the danger of a direct contacting of the material and wear of material and, in the extreme case, danger of breakage of the sealing device, as in the case of conventional labyrinth seals. However, as a result of a continuous frictional contacting, a brush sealing device as well as its pertaining counterface (rotor) is also subjected to extensive material wear, for which, among other things, special coatings have been suggested on the rotor side. However, in each of these cases, an abrasion of the brush or the coating must be expected which leads to considerable impurities in the media to be sealed off. The quality, the wear and the abrasion of the brush sealing devices, among other things, depend significantly on the selection of the material for the bristles of the sealing device. For this purpose, locally different bristle materials are known in that an elastic bristle core (glass, metal, plastic) is to be coated in complicated coating processes (PVD, CVD) with materials (such as gold, silver, nickel) which are as abrasion-resistant as possible, but expensive (see German Patent DE-PS 3429708).
In addition, radial slide ring sealing devices are known by themselves which basically consist of a housing, the sliding ring, an element which is elastic in axial direction and of the pertaining shaft or the pertaining shaft section. In this case, the sliding ring is sealingly guided in the housing between a supporting shoulder of the housing on one side and a spring plate which, for example, is movable on the other side under the effect of the spring element (secondary sealing). As the primary sealing, a relatively small radial sealing gap is to be maintained between the sliding ring and the shaft.
In addition to having a comparatively expensive and trouble-prone construction, sliding ring sealing devices of this type have the disadvantage of a comparatively high sealing leakage flow, particularly, if, in view of nonsteady operating conditions, comparably large radial gaps (primary sealing) must be taken into account in order to in turn counteract a wear caused by a mutual material contacting between the sliding ring and shaft.
Such radial sliding ring sealing devices cannot meet any perfect sealing requirements, particularly if the object is a sealing-off of bearing spaces in gas turbines with respect to the engine inlet or the local ambient air surroundings or with respect to the exhaust flow, thus bearing spaces which normally have a significantly lower pressure level than the bearing space in front of the sealing device.
Sliding ring sealing concepts in a multiple arrangement behind one another (labyrinth construction) which have been suggested in order to eliminate this deficiency, have the additional disadvantage of a considerable installation space requirement.
An object of the invention to provide a sealing device of the initially mentioned type which, while utilizing the advantages of a brush sealing concept (among others, suspension, damping), operates practically without any wear and therefore without any abrasion. Within the scope of this object, a sealing device will therefore be provided which is suitable for the perfect sealing-off of spaces acted upon by media, such as fluids and/or gases with comparatively high differential pressures, and, at the same time, is characterized by a comparatively small installation volume and a comparatively simple and trouble free construction.
This object is achieved according to the invention by providing an arrangement with at least one sliding sealing ring surrounding a rotor shaft and at least one brush sealing device fixedly held at a stator and having free brush bristle ends sealingly guided in the at least one sliding sealing ring. Thus a basic idea of the invention relates to an advantageous combination of a brush sealing device and a radial sliding ring sealing device. The sealing device is constructed such that the shaft with the at least one radial sliding ring represents the primary sealing point or primary sealing. The sliding ring is equipped at the circumference with at least one point of separation and is elastically disposed at the inside diameter of the bristles of the brush sealing device. Thus, together with the brush bundle, the sliding ring forms the secondary sealing point or secondary sealing. By means of a slight overlapping of the bristles of the brush sealing device at their open bristle ends or at the inside diameter, the sliding ring can rest in the inoperative position against the shaft circumference.
When the shaft rotates, an aerodynamic pressure or pressure cushion can therefore build up in the primary sealing gap which keeps the frictional losses of the sliding ring to a minimum. Radial rotor deflections are absorbed and damped by way of the bristles of the brush sealing device which are constructed as a springing element.
Basically, both rotating directions of the shaft are possible with certain preferred embodiments of the invention. In this case, the sliding ring is prevented from rotating along by the frictional forces of the bristles. However, when the shaft is rotated in the direction of the respective brush incidence or the respective angle of brush incidence, it may slowly move into the rotating direction. "brush incidence" means that, when the sealing device is arranged in a common axial plane, the bristles are set with respect to a radial plane of symmetry, with respect to a stator/rotor axis, in each case in a diagonal cut of the mentioned plane over the circumference of the sealing device. The pressure to be sealed off causes the sliding ring to axially place itself at the brush bundle. Thus, in addition, to a higher frictional force, an optimum packing density of the brush sealing device is achieved which has a very favorable effect on the leakage of the sealing device (secondary sealing).
In order to control the comparatively high pressure differences, several sealing devices may be arranged next to one another. By means of the suitable construction of the sliding ring, a changing pressure admission at the sealing unit can be controlled.
By means of the sealing device according to the invention, the following advantages are achieved with respect to manufacturing and operating characteristics:
Simpler and More Cost-Effective Manufacturing of the Brush Sealing Device
In the case of a conventionally constructed brush sealing device (see German Published Unexamined Patent Application OS-E-30 206), much attention must be paid to the packing density of the bristles. This is no longer necessary now that a good packing density is achieved by wa of the differential pressure by means of the sliding ring at the bristles of the brush sealing device.
The bristle ends no longer have to be smoothed. The brush diameter may be dimensioned by means of punching or eroding.
Since the brush does not contact any rotating component, it is sufficient to select a material of a lower quality.
The angle of incidence of the bristles of the brush sealing device may be selected to be relatively small and have a tolerance range which is higher in comparison to conventional concepts.
Simpler and More Cost-Effective Manufacturing of the Rotor Surface
Ceramic starting coatings are not required. No contamination of the oil for example takes place by ceramic abrasion in the case of bearing chamber sealing devices. A hardened, nitrified or chrome-plated surface is sufficient.
Facilitated Handling
The bristle ends are well protected by the sliding ring.
During the mounting and the operation, both rotating directions are basically possible.
Lower Cost of Repairing the Sealing Device
The brush is not subjected to wear.
The sliding ring can be manufactured at low cost and can be exchanged easily.
Optimal Operating Characteristics
An aerodynamic pressure builds up between the sliding ring and the shaft which considerably reduces the frictional losses. As a result of the slotted sliding ring, the gap can adjust itself (primary sealing).
The bristles of the brush sealing device are used as a secondary sealing and as a spring/damper. The spring/damper can be optimally adjusted, specifically by, for example, a varying packing density of the bristles (overlapping density of the free bristle ends at the inside diameter of the brush sealing device; selection of the initially defined angle of incidence of the bristles, or variable packing density or the given number of bristles with respect to the outside and inside diameter of the bristles of the brush sealing device).
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.